//: C20:Ring.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Making a "ring" data structure from the STL
#include <iostream>
#include <list>
#include <string>
using namespace std;

template<class T>
class Ring
{
    list<T> lst;
public:
    // Declaration necessary so the following
    // 'friend' statement sees this 'iterator'
    // instead of std::iterator:
    class iterator;
    friend class iterator;
    class iterator : public std::iterator<
            std::bidirectional_iterator_tag,T,ptrdiff_t>
    {
        list<T>::iterator it;
        list<T>* r;
    public:
        // "typename" necessary to resolve nesting:
        iterator(list<T>& lst,
                 const typename list<T>::iterator& i)
                : r(&lst), it(i) {}
        bool operator==(const iterator& x) const {
            return it == x.it;
        }
        bool operator!=(const iterator& x) const {
            return !(*this == x);
        }
        list<T>::reference operator*() const {
            return *it;
        }
        iterator& operator++() {
            ++it;
            if (it == r->end())
                it = r->begin();
            return *this;
        }
        iterator operator++(int) {
            iterator tmp = *this;
            ++*this;
            return tmp;
        }
        iterator& operator--() {
            if (it == r->begin())
                it = r->end();
            --it;
            return *this;
        }
        iterator operator--(int) {
            iterator tmp = *this;
            --*this;
            return tmp;
        }
        iterator insert(const T& x) {
            return iterator(*r, r->insert(it, x));
        }
        iterator erase() {
            return iterator(*r, r->erase(it));
        }
    };
    void push_back(const T& x) {
        lst.push_back(x);
    }
    iterator begin() {
        return iterator(lst, lst.begin());
    }
    int size() {
        return lst.size();
    }
};

int main()
{
    Ring<string> rs;
    rs.push_back("one");
    rs.push_back("two");
    rs.push_back("three");
    rs.push_back("four");
    rs.push_back("five");
    Ring<string>::iterator it = rs.begin();
    it++;
    it++;
    it.insert("six");
    it = rs.begin();
    // Twice around the ring:
    for (int i = 0; i < rs.size() * 2; i++)
        cout << *it++ << endl;
} ///:~
